Abstract 2224A: A novel TNFRSF25 agonist, PTX35, synergizes with Gp96-Ig/OX40L-Ig to enhance effector and memory anti-tumor CD8+ T cell responses and delay tumor growth

We have developed a next generation cellular vaccine platform that incorporates a tumor antigen chaperone (gp96-Ig) in a tumor cell line and a host of over-expressed cancer associated neoantigens. Viagenpumatucel-L (HS-110), a human lung adenocarcinoma cell line, stably transfected to express gp96-Ig, is being tested in a phase 1/2 clinical trial (NCT#02439450) for NSCLC. Heat has recently developed HS-130, an allogeneic cell-based vaccine, designed to secrete tumor-associated antigens along with a costimulatory molecule, OX40L-Fc. Preclinical results of mouse HS-130 (mHS-130) in combination with mouse HS-110 (mHS-110) has shown a potent anti-tumor effector and memory CD8+ T cell response, followed by tumor regression. In our current study, we further characterized the role of mHS-110 and mHS-130 in combination with an agonist TNFRSF25 monoclonal antibody (mAb), PTX-35. PTX-35 is a potent stimulator of effector and memory CD8+ T cell responses, which taken together with HS-110 and HS130 has the potential of treating human cancers. To study expansion, contraction, and maintenance of tumor-specific CD8+ T cell responses, mHS-110 and/or mHS-130, in combination with different doses of mouse-IgG1-PTX-35 (mPTX-35) was administered to C57BL/6 mice that were adoptively transferred with syngeneic OVA-specific T cells (OT-I). Mice were then challenged with murine melanoma tumors (B16F10-OVA) to characterize the tumor-specific immune cells in the periphery, spleen, and tumor-microenvironment that were involved in tumor regression. Combination of mPTX-35 with mHS-110 and mHS-130 increased the expansion of tumor-specific CD8+ T-cells, in a mPTX-35 dose-dependent manner. This cellular expansion was significantly higher in the 1 mg/kg dose of mPTX-35 and far exceeded the additive value of mPTX-35, mHS-130, and mHS-110 treatment alone. Systemic administration of mPTX-35, in combination with mHS-110 and mHS-130, led to a significant increase in the expansion of activated CD8+ T cells in the blood and stimulated activation of effector memory CD8+ T cells residing in the spleen. Importantly, this combination resulted in higher frequencies of tumor infiltrating lymphocytes (TILs), which enhanced regression of established B16F10-OVA tumors and increased overall survival. These results strongly suggest that mPTX-35 synergizes with mHS-110 and mHS-130 to amplify activated tumor-specific CD8+ T cells, program a strong memory response, and allow for tumor regression. We also asses